The present invention relates to means for the distribution of a liquid active material, such as a perfume, air freshener, insecticide formulation, or other material, in the form of fine particles or droplets, as in a fine spray, by means of a piezoelectric device. In particular, the invention is directed to a piezoelectric liquid delivery system for production of droplets of liquid, or liquid suspensions, by means of an electromechanical or electroacoustical actuator. More specifically, the present invention relates to a battery operated dispenser utilizing an orifice plate in communication with a piezoelectric element. By control of the viscosity and surface tension of the liquid to be dispersed, an improved method of dispensing such liquids is achieved.
The distribution of liquids by formation of a fine spray, or atomization, is well known. One method for such distribution is to atomize a liquid by means of the acoustic vibration generated by an ultrasonic piezoelectric vibrator. An example of such a method is shown in Carter, U.S. Pat. No. 4,702,418, which discloses an aerosol dispenser including a nozzle chamber for holding fluid to be dispensed and a diaphragm forming at least a portion of the chamber. An aerosol dispensing nozzle is disposed therein, with a restrictive passage for introducing liquid from the reservoir to the nozzle. A pulse generator in combination with a low voltage power source is used to drive a piezoelectric bender, which drives fluid from the reservoir through the nozzle to create an aerosol spray.
Another atomizer spraying device is shown by Humberstone et al, in U.S. Pat. No. 5,518,179, which teaches a liquid droplet production apparatus comprising a membrane which is vibrated by an actuator which has a composite thin-walled structure, and is arranged to operate in a bending mode. Liquid is supplied directly to a surface of the membrane and sprayed therefrom in fine droplets upon vibration of the membrane.
U.S. Pat. Nos. 5,297,734 and 5,657,926, of Toda, teach ultrasonic atomizing devices comprising piezoelectric vibrators with a vibrating plate connected thereto. In U.S. Pat. No. 5,297,734, the vibrating plate is described as having a large number of minute holes therein for passage of the liquid.
While a number of additional patents disclose means for the dispersion of liquids by ultrasonic atomization, or for timed intervals of dispersion, they have achieved only moderate success in the efficient atomization of such materials as perfumes. See, for example, U.S. Pat. Nos. 3,543,122, 3,615,041, 4,479,609, 4,533,082, and 4,790,479. The disclosures of these patents, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
Such atomizers fail to provide an easily portable, battery operated dispenser employing an orifice plate in mechanical connection with a piezoelectric element, capable of long periods of use with little or no variation in the delivery rate. Thus, a need exists for improved atomizers or dispensers for use in distribution of active fluids such as fragrances and insecticides, which atomizers are highly efficient and consume minimal electrical power while providing wide dispersal of the liquid.
A primary purpose of the present invention is to provide a highly efficient method for dispensing such liquids as perfumes, air fresheners, or other liquids. Such other liquids include household cleaning materials, sanitizers, disinfectants, repellants, insecticides, aroma therapy formulations, medicinals, therapeutic liquids, or other liquids or liquid suspensions which benefit from atomization for use. These compositions may be aqueous, or comprise various solvents.
It is an object of the present invention to provide an easily portable, battery operated dispenser employing a domed orifice plate in mechanical connection with a piezoelectric element. It is a further object to provide a piezoelectric pump capable of operating efficiently for months, on low voltage batteries, while maintaining consistency of delivery throughout the period. Included in such object is to provide a piezoelectric atomizer capable for use with such electrical sources as 9 volt batteries, conventional dry cells such as xe2x80x9cAxe2x80x9d, xe2x80x9cAAxe2x80x9d, xe2x80x9cAAAxe2x80x9d, xe2x80x9cCxe2x80x9d, and xe2x80x9cDxe2x80x9d cells, button cells, watch batteries, and solar cells. The preferred energy sources for utilization in combination with the present invention are xe2x80x9cAAxe2x80x9d and xe2x80x9cAAAxe2x80x9d cells.
In still another object, it is desired to provide a liquid delivery system capable of atomizing such liquids as fragrance oil or insecticide formulations linearly over time, while maintaining the same character/composition on the last day as was delivered on the first, i.e. with no component change or separation with time. The electronics of such a unit may be programmable, and may be used to set a precise delivery rate (in milligrams per hour, hereinafter mg/hr). Alternatively, the electronic circuitry may allow the consumer to adjust intensity or effectiveness to a desired level for personal preference, efficacy, or for room size.
Another object of this invention is to provide small particles of pure fragrance or insecticide formulation which may be propelled intermittently from the unit to form a small xe2x80x9ccloudxe2x80x9d or xe2x80x9cpuff,xe2x80x9d which particles quickly diffuse and move throughout a large area on air currents present in said area. It is found that the small size of such particles, and the correspondingly large ratio of surface area to mass, result in these liquid particles evaporating quickly and uniformly. In preferred embodiments, the delivery system operates with a linear delivery rate for several months on a single 1.5 volt xe2x80x9cAAxe2x80x9d size battery, delivering uniform volumes of essentially equally sized droplets of the liquid for the entire period.
In the preferred embodiment of the present invention, these and other objects of this invention are achieved by an atomizer for fragrances, insecticide formulations, and other liquids such as set forth previously, wherein the atomization system includes a chamber for the liquid to be dispensed, means to supply the liquid from said chamber to an orifice plate for dispersal of the liquid, a piezoelectric element, an energy source, and circuitry to drive and control the piezoelectric element. The fragrance, insecticide formulation, or other desired liquid is supplied to the back side of the orifice plate through a liquid transport means such as a capillary feed system that delivers the liquid in surface tension contact with the plate The piezoelectric element may be driven by circuitry powered by a small battery, causing the element to vibrate and forcing liquid through the orifice plate, which has one or more small tapered or conical holes therein, perpendicular to the surfaces thereof, the exit of said holes being on the order of from about 1 to about 25 microns, preferably from about 4 to about 10 microns, and most preferably from about 5 to about 7 microns in diameter. It has been found that by limiting the use of liquids to those which exhibit viscosity below 10 centipoise, and which have surface tensions below about 35, and preferably in the range of from about 20 to about 30 dynes per centimeter, superior results are attained. The present invention thus provides a means for uniform atomization of the liquid to be dispensed throughout the total period of dispersion, such that the amount dispersed per time unit at the commencement of dispersion does not vary from the amount dispersed near or at the finish of dispersion. Viscosity is in centipoise, as determined using the Bohlin CVO Rheometer system in conjunction with a high sensitivity double gap geometry. Surface Tension results, in dynes per centimeter, were generated using the Kruss K-12 tensionmeter operating under the Wilhelmy Plate protocol. These and still other objects and advantages of the present invention will be apparent from the description which follows, which is, however, merely of the preferred embodiments. Thus, the claims should be looked to in order to understand the full scope of the invention.